how do you find this formula?

The argument isn't being assigned to a function. The function name required by the kata (stringToNumber) is being assigned to an existing function. This is similar:
var rand = Math.random

now you have a function, rand, that can do the same thing Math.random can.

Woah that's cool. I didn't know argument could be asigned to a function and the function would be performed on it.

one dot is for decimal and other is access

wait, how it works?

oooohh, now i understand. thank you!

i don't understand, how does this work?

What the...
hello world in another level

wow, that's super weird